/*
 * INET         An implementation of the TCP/IP protocol suite for the LINUX
 *              operating system.  INET is implemented using the  BSD Socket
 *              interface as the means of communication with the user level.
 *
 *              The IP fragmentation functionality.
 *
 * Authors:     Fred N. van Kempen <waltje@uWalt.NL.Mugnet.ORG>
 *              Alan Cox <alan@lxorguk.ukuu.org.uk>
 *
 * Fixes:
 *              Alan Cox        :       Split from ip.c , see ip_input.c for history.
 *              David S. Miller :       Begin massive cleanup...
 *              Andi Kleen      :       Add sysctls.
 *              xxxx            :       Overlapfrag bug.
 *              Ultima          :       ip_expire() kernel panic.
 *              Bill Hawes      :       Frag accounting and evictor fixes.
 *              John McDonald   :       0 length frag bug.
 *              Alexey Kuznetsov:       SMP races, threading, cleanup.
 *              Patrick McHardy :       LRU queue of frag heads for evictor.
 */

#include <linux/compiler.h>
#include <linux/module.h>
#include <linux/types.h>
#include <linux/mm.h>
#include <linux/jiffies.h>
#include <linux/skbuff.h>
#include <linux/list.h>
#include <linux/ip.h>
#include <linux/icmp.h>
#include <linux/netdevice.h>
#include <linux/jhash.h>
#include <linux/random.h>
#include <net/sock.h>
#include <net/ip.h>
#include <net/icmp.h>
#include <net/checksum.h>
#include <net/inetpeer.h>
#include <net/inet_frag.h>
#include <linux/tcp.h>
#include <linux/udp.h>
#include <linux/inet.h>
#include <linux/netfilter_ipv4.h>

/* NOTE. Logic of IP defragmentation is parallel to corresponding IPv6
 * code now. If you change something here, _PLEASE_ update ipv6/reassembly.c
 * as well. Or notify me, at least. --ANK
 */

static int sysctl_ipfrag_max_dist __read_mostly = 64;

struct ipfrag_skb_cb
{
        struct inet_skb_parm    h;
        int                     offset;
};

#define FRAG_CB(skb)    ((struct ipfrag_skb_cb *)((skb)->cb))

/* Describe an entry in the "incomplete datagrams" queue. */
struct ipq {
        struct inet_frag_queue q;

        u32             user;
        __be32          saddr;
        __be32          daddr;
        __be16          id;
        u8              protocol;
        int             iif;
        unsigned int    rid;
        struct inet_peer *peer;
};

static struct inet_frags ip4_frags;

int ip_frag_nqueues(struct net *net)
{
        return net->ipv4.frags.nqueues;
}

int ip_frag_mem(struct net *net)
{
        return atomic_read(&net->ipv4.frags.mem);
}

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
                         struct net_device *dev);

struct ip4_create_arg {
        struct iphdr *iph;
        u32 user;
};

static unsigned int ipqhashfn(__be16 id, __be32 saddr, __be32 daddr, u8 prot)
{
        return jhash_3words((__force u32)id << 16 | prot,
                            (__force u32)saddr, (__force u32)daddr,
                            ip4_frags.rnd) & (INETFRAGS_HASHSZ - 1);
}

static unsigned int ip4_hashfn(struct inet_frag_queue *q)
{
        struct ipq *ipq;

        ipq = container_of(q, struct ipq, q);
        return ipqhashfn(ipq->id, ipq->saddr, ipq->daddr, ipq->protocol);
}

static int ip4_frag_match(struct inet_frag_queue *q, void *a)
{
        struct ipq *qp;
        struct ip4_create_arg *arg = a;

        qp = container_of(q, struct ipq, q);
        return (qp->id == arg->iph->id &&
                        qp->saddr == arg->iph->saddr &&
                        qp->daddr == arg->iph->daddr &&
                        qp->protocol == arg->iph->protocol &&
                        qp->user == arg->user);
}

/* Memory Tracking Functions. */
static __inline__ void frag_kfree_skb(struct netns_frags *nf,
                struct sk_buff *skb, int *work)
{
        if (work)
                *work -= skb->truesize;
        atomic_sub(skb->truesize, &nf->mem);
        kfree_skb(skb);
}

static void ip4_frag_init(struct inet_frag_queue *q, void *a)
{
        struct ipq *qp = container_of(q, struct ipq, q);
        struct ip4_create_arg *arg = a;

        qp->protocol = arg->iph->protocol;
        qp->id = arg->iph->id;
        qp->saddr = arg->iph->saddr;
        qp->daddr = arg->iph->daddr;
        qp->user = arg->user;
        qp->peer = sysctl_ipfrag_max_dist ?
                inet_getpeer(arg->iph->saddr, 1) : NULL;
}

static __inline__ void ip4_frag_free(struct inet_frag_queue *q)
{
        struct ipq *qp;

        qp = container_of(q, struct ipq, q);
        if (qp->peer)
                inet_putpeer(qp->peer);
}


/* Destruction primitives. */

static __inline__ void ipq_put(struct ipq *ipq)
{
        inet_frag_put(&ipq->q, &ip4_frags);
}

/* Kill ipq entry. It is not destroyed immediately,
 * because caller (and someone more) holds reference count.
 */
static void ipq_kill(struct ipq *ipq)
{
        inet_frag_kill(&ipq->q, &ip4_frags);
}

/* Memory limiting on fragments.  Evictor trashes the oldest
 * fragment queue until we are back under the threshold.
 */
static void ip_evictor(struct net *net)
{
        int evicted;

        evicted = inet_frag_evictor(&net->ipv4.frags, &ip4_frags);
        if (evicted)
                IP_ADD_STATS_BH(net, IPSTATS_MIB_REASMFAILS, evicted);
}

/*
 * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
 */
static void ip_expire(unsigned long arg)
{
        struct ipq *qp;
        struct net *net;

        qp = container_of((struct inet_frag_queue *) arg, struct ipq, q);
        net = container_of(qp->q.net, struct net, ipv4.frags);

        spin_lock(&qp->q.lock);

        if (qp->q.last_in & INET_FRAG_COMPLETE)
                goto out;

        ipq_kill(qp);

        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMTIMEOUT);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);

        if ((qp->q.last_in & INET_FRAG_FIRST_IN) && qp->q.fragments != NULL) {
                struct sk_buff *head = qp->q.fragments;

                /* Send an ICMP "Fragment Reassembly Timeout" message. */
                if ((head->dev = dev_get_by_index(net, qp->iif)) != NULL) {
                        icmp_send(head, ICMP_TIME_EXCEEDED, ICMP_EXC_FRAGTIME, 0);
                        dev_put(head->dev);
                }
        }
out:
        spin_unlock(&qp->q.lock);
        ipq_put(qp);
}

/* Find the correct entry in the "incomplete datagrams" queue for
 * this IP datagram, and create new one, if nothing is found.
 */
static inline struct ipq *ip_find(struct net *net, struct iphdr *iph, u32 user)
{
        struct inet_frag_queue *q;
        struct ip4_create_arg arg;
        unsigned int hash;

        arg.iph = iph;
        arg.user = user;

        read_lock(&ip4_frags.lock);
        hash = ipqhashfn(iph->id, iph->saddr, iph->daddr, iph->protocol);

        q = inet_frag_find(&net->ipv4.frags, &ip4_frags, &arg, hash);
        if (q == NULL)
                goto out_nomem;

        return container_of(q, struct ipq, q);

out_nomem:
        LIMIT_NETDEBUG(KERN_ERR "ip_frag_create: no memory left !\n");
        return NULL;
}

/* Is the fragment too far ahead to be part of ipq? */
static inline int ip_frag_too_far(struct ipq *qp)
{
        struct inet_peer *peer = qp->peer;
        unsigned int max = sysctl_ipfrag_max_dist;
        unsigned int start, end;

        int rc;

        if (!peer || !max)
                return 0;

        start = qp->rid;
        end = atomic_inc_return(&peer->rid);
        qp->rid = end;

        rc = qp->q.fragments && (end - start) > max;

        if (rc) {
                struct net *net;

                net = container_of(qp->q.net, struct net, ipv4.frags);
                IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        }

        return rc;
}

static int ip_frag_reinit(struct ipq *qp)
{
        struct sk_buff *fp;

        if (!mod_timer(&qp->q.timer, jiffies + qp->q.net->timeout)) {
                atomic_inc(&qp->q.refcnt);
                return -ETIMEDOUT;
        }

        fp = qp->q.fragments;
        do {
                struct sk_buff *xp = fp->next;
                frag_kfree_skb(qp->q.net, fp, NULL);
                fp = xp;
        } while (fp);

        qp->q.last_in = 0;
        qp->q.len = 0;
        qp->q.meat = 0;
        qp->q.fragments = NULL;
        qp->iif = 0;

        return 0;
}

/* Add new segment to existing queue. */
static int ip_frag_queue(struct ipq *qp, struct sk_buff *skb)
{
        struct sk_buff *prev, *next;
        struct net_device *dev;
        int flags, offset;
        int ihl, end;
        int err = -ENOENT;

        if (qp->q.last_in & INET_FRAG_COMPLETE)
                goto err;

        if (!(IPCB(skb)->flags & IPSKB_FRAG_COMPLETE) &&
            unlikely(ip_frag_too_far(qp)) &&
            unlikely(err = ip_frag_reinit(qp))) {
                ipq_kill(qp);
                goto err;
        }

        offset = ntohs(ip_hdr(skb)->frag_off);
        flags = offset & ~IP_OFFSET;
        offset &= IP_OFFSET;
        offset <<= 3;           /* offset is in 8-byte chunks */
        ihl = ip_hdrlen(skb);

        /* Determine the position of this fragment. */
        end = offset + skb->len - ihl;
        err = -EINVAL;

        /* Is this the final fragment? */
        if ((flags & IP_MF) == 0) {
                /* If we already have some bits beyond end
                 * or have different end, the segment is corrrupted.
                 */
                if (end < qp->q.len ||
                    ((qp->q.last_in & INET_FRAG_LAST_IN) && end != qp->q.len))
                        goto err;
                qp->q.last_in |= INET_FRAG_LAST_IN;
                qp->q.len = end;
        } else {
                if (end&7) {
                        end &= ~7;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
                if (end > qp->q.len) {
                        /* Some bits beyond end -> corruption. */
                        if (qp->q.last_in & INET_FRAG_LAST_IN)
                                goto err;
                        qp->q.len = end;
                }
        }
        if (end == offset)
                goto err;

        err = -ENOMEM;
        if (pskb_pull(skb, ihl) == NULL)
                goto err;

        err = pskb_trim_rcsum(skb, end - offset);
        if (err)
                goto err;

        /* Find out which fragments are in front and at the back of us
         * in the chain of fragments so far.  We must know where to put
         * this fragment, right?
         */
        prev = NULL;
        for (next = qp->q.fragments; next != NULL; next = next->next) {
                if (FRAG_CB(next)->offset >= offset)
                        break;  /* bingo! */
                prev = next;
        }

        /* We found where to put this one.  Check for overlap with
         * preceding fragment, and, if needed, align things so that
         * any overlaps are eliminated.
         */
        if (prev) {
                int i = (FRAG_CB(prev)->offset + prev->len) - offset;

                if (i > 0) {
                        offset += i;
                        err = -EINVAL;
                        if (end <= offset)
                                goto err;
                        err = -ENOMEM;
                        if (!pskb_pull(skb, i))
                                goto err;
                        if (skb->ip_summed != CHECKSUM_UNNECESSARY)
                                skb->ip_summed = CHECKSUM_NONE;
                }
        }

        err = -ENOMEM;

        while (next && FRAG_CB(next)->offset < end) {
                int i = end - FRAG_CB(next)->offset; /* overlap is 'i' bytes */

                if (i < next->len) {
                        /* Eat head of the next overlapped fragment
                         * and leave the loop. The next ones cannot overlap.
                         */
                        if (!pskb_pull(next, i))
                                goto err;
                        FRAG_CB(next)->offset += i;
                        qp->q.meat -= i;
                        if (next->ip_summed != CHECKSUM_UNNECESSARY)
                                next->ip_summed = CHECKSUM_NONE;
                        break;
                } else {
                        struct sk_buff *free_it = next;

                        /* Old fragment is completely overridden with
                         * new one drop it.
                         */
                        next = next->next;

                        if (prev)
                                prev->next = next;
                        else
                                qp->q.fragments = next;

                        qp->q.meat -= free_it->len;
                        frag_kfree_skb(qp->q.net, free_it, NULL);
                }
        }

        FRAG_CB(skb)->offset = offset;

        /* Insert this fragment in the chain of fragments. */
        skb->next = next;
        if (prev)
                prev->next = skb;
        else
                qp->q.fragments = skb;

        dev = skb->dev;
        if (dev) {
                qp->iif = dev->ifindex;
                skb->dev = NULL;
        }
        qp->q.stamp = skb->tstamp;
        qp->q.meat += skb->len;
        atomic_add(skb->truesize, &qp->q.net->mem);
        if (offset == 0)
                qp->q.last_in |= INET_FRAG_FIRST_IN;

        if (qp->q.last_in == (INET_FRAG_FIRST_IN | INET_FRAG_LAST_IN) &&
            qp->q.meat == qp->q.len)
                return ip_frag_reasm(qp, prev, dev);

        write_lock(&ip4_frags.lock);
        list_move_tail(&qp->q.lru_list, &qp->q.net->lru_list);
        write_unlock(&ip4_frags.lock);
        return -EINPROGRESS;

err:
        kfree_skb(skb);
        return err;
}


/* Build a new IP datagram from all its fragments. */

static int ip_frag_reasm(struct ipq *qp, struct sk_buff *prev,
                         struct net_device *dev)
{
        struct net *net = container_of(qp->q.net, struct net, ipv4.frags);
        struct iphdr *iph;
        struct sk_buff *fp, *head = qp->q.fragments;
        int len;
        int ihlen;
        int err;

        ipq_kill(qp);

        /* Make the one we just received the head. */
        if (prev) {
                head = prev->next;
                fp = skb_clone(head, GFP_ATOMIC);
                if (!fp)
                        goto out_nomem;

                fp->next = head->next;
                prev->next = fp;

                skb_morph(head, qp->q.fragments);
                head->next = qp->q.fragments->next;

                kfree_skb(qp->q.fragments);
                qp->q.fragments = head;
        }

        WARN_ON(head == NULL);
        WARN_ON(FRAG_CB(head)->offset != 0);

        /* Allocate a new buffer for the datagram. */
        ihlen = ip_hdrlen(head);
        len = ihlen + qp->q.len;

        err = -E2BIG;
        if (len > 65535)
                goto out_oversize;

        /* Head of list must not be cloned. */
        if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
                goto out_nomem;

        /* If the first fragment is fragmented itself, we split
         * it to two chunks: the first with data and paged part
         * and the second, holding only fragments. */
        if (skb_has_frags(head)) {
                struct sk_buff *clone;
                int i, plen = 0;

                if ((clone = alloc_skb(0, GFP_ATOMIC)) == NULL)
                        goto out_nomem;
                clone->next = head->next;
                head->next = clone;
                skb_shinfo(clone)->frag_list = skb_shinfo(head)->frag_list;
                skb_frag_list_init(head);
                for (i=0; i<skb_shinfo(head)->nr_frags; i++)
                        plen += skb_shinfo(head)->frags[i].size;
                clone->len = clone->data_len = head->data_len - plen;
                head->data_len -= clone->len;
                head->len -= clone->len;
                clone->csum = 0;
                clone->ip_summed = head->ip_summed;
                atomic_add(clone->truesize, &qp->q.net->mem);
        }

        skb_shinfo(head)->frag_list = head->next;
        skb_push(head, head->data - skb_network_header(head));
        atomic_sub(head->truesize, &qp->q.net->mem);

        for (fp=head->next; fp; fp = fp->next) {
                head->data_len += fp->len;
                head->len += fp->len;
                if (head->ip_summed != fp->ip_summed)
                        head->ip_summed = CHECKSUM_NONE;
                else if (head->ip_summed == CHECKSUM_COMPLETE)
                        head->csum = csum_add(head->csum, fp->csum);
                head->truesize += fp->truesize;
                atomic_sub(fp->truesize, &qp->q.net->mem);
        }

        head->next = NULL;
        head->dev = dev;
        head->tstamp = qp->q.stamp;

        iph = ip_hdr(head);
        iph->frag_off = 0;
        iph->tot_len = htons(len);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMOKS);
        qp->q.fragments = NULL;
        return 0;

out_nomem:
        LIMIT_NETDEBUG(KERN_ERR "IP: queue_glue: no memory for gluing "
                              "queue %p\n", qp);
        err = -ENOMEM;
        goto out_fail;
out_oversize:
        if (net_ratelimit())
                printk(KERN_INFO "Oversized IP packet from %pI4.\n",
                        &qp->saddr);
out_fail:
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        return err;
}

/* Process an incoming IP datagram fragment. */
int ip_defrag(struct sk_buff *skb, u32 user)
{
        struct ipq *qp;
        struct net *net;

        net = skb->dev ? dev_net(skb->dev) : dev_net(skb_dst(skb)->dev);
        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMREQDS);

        /* Start by cleaning up the memory. */
        if (atomic_read(&net->ipv4.frags.mem) > net->ipv4.frags.high_thresh)
                ip_evictor(net);

        /* Lookup (or create) queue header */
        if ((qp = ip_find(net, ip_hdr(skb), user)) != NULL) {
                int ret;

                spin_lock(&qp->q.lock);

                ret = ip_frag_queue(qp, skb);

                spin_unlock(&qp->q.lock);
                ipq_put(qp);
                return ret;
        }

        IP_INC_STATS_BH(net, IPSTATS_MIB_REASMFAILS);
        kfree_skb(skb);
        return -ENOMEM;
}

#ifdef CONFIG_SYSCTL
static int zero;

static struct ctl_table ip4_frags_ns_ctl_table[] = {
        {
                .ctl_name       = NET_IPV4_IPFRAG_HIGH_THRESH,
                .procname       = "ipfrag_high_thresh",
                .data           = &init_net.ipv4.frags.high_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec
        },
        {
                .ctl_name       = NET_IPV4_IPFRAG_LOW_THRESH,
                .procname       = "ipfrag_low_thresh",
                .data           = &init_net.ipv4.frags.low_thresh,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec
        },
        {
                .ctl_name       = NET_IPV4_IPFRAG_TIME,
                .procname       = "ipfrag_time",
                .data           = &init_net.ipv4.frags.timeout,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
                .strategy       = sysctl_jiffies
        },
        { }
};

static struct ctl_table ip4_frags_ctl_table[] = {
        {
                .ctl_name       = NET_IPV4_IPFRAG_SECRET_INTERVAL,
                .procname       = "ipfrag_secret_interval",
                .data           = &ip4_frags.secret_interval,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_jiffies,
                .strategy       = sysctl_jiffies
        },
        {
                .procname       = "ipfrag_max_dist",
                .data           = &sysctl_ipfrag_max_dist,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec_minmax,
                .extra1         = &zero
        },
        { }
};

static int ip4_frags_ns_ctl_register(struct net *net)
{
        struct ctl_table *table;
        struct ctl_table_header *hdr;

        table = ip4_frags_ns_ctl_table;
        if (net != &init_net) {
                table = kmemdup(table, sizeof(ip4_frags_ns_ctl_table), GFP_KERNEL);
                if (table == NULL)
                        goto err_alloc;

                table[0].data = &net->ipv4.frags.high_thresh;
                table[1].data = &net->ipv4.frags.low_thresh;
                table[2].data = &net->ipv4.frags.timeout;
        }

        hdr = register_net_sysctl_table(net, net_ipv4_ctl_path, table);
        if (hdr == NULL)
                goto err_reg;

        net->ipv4.frags_hdr = hdr;
        return 0;

err_reg:
        if (net != &init_net)
                kfree(table);
err_alloc:
        return -ENOMEM;
}

static void ip4_frags_ns_ctl_unregister(struct net *net)
{
        struct ctl_table *table;

        table = net->ipv4.frags_hdr->ctl_table_arg;
        unregister_net_sysctl_table(net->ipv4.frags_hdr);
        kfree(table);
}

static void ip4_frags_ctl_register(void)
{
        register_net_sysctl_rotable(net_ipv4_ctl_path, ip4_frags_ctl_table);
}
#else
static inline int ip4_frags_ns_ctl_register(struct net *net)
{
        return 0;
}

static inline void ip4_frags_ns_ctl_unregister(struct net *net)
{
}

static inline void ip4_frags_ctl_register(void)
{
}
#endif

static int ipv4_frags_init_net(struct net *net)
{
        /*
         * Fragment cache limits. We will commit 256K at one time. Should we
         * cross that limit we will prune down to 192K. This should cope with
         * even the most extreme cases without allowing an attacker to
         * measurably harm machine performance.
         */
        net->ipv4.frags.high_thresh = 256 * 1024;
        net->ipv4.frags.low_thresh = 192 * 1024;
        /*
         * Important NOTE! Fragment queue must be destroyed before MSL expires.
         * RFC791 is wrong proposing to prolongate timer each fragment arrival
         * by TTL.
         */
        net->ipv4.frags.timeout = IP_FRAG_TIME;

        inet_frags_init_net(&net->ipv4.frags);

        return ip4_frags_ns_ctl_register(net);
}

static void ipv4_frags_exit_net(struct net *net)
{
        ip4_frags_ns_ctl_unregister(net);
        inet_frags_exit_net(&net->ipv4.frags, &ip4_frags);
}

static struct pernet_operations ip4_frags_ops = {
        .init = ipv4_frags_init_net,
        .exit = ipv4_frags_exit_net,
};

void __init ipfrag_init(void)
{
        ip4_frags_ctl_register();
        register_pernet_subsys(&ip4_frags_ops);
        ip4_frags.hashfn = ip4_hashfn;
        ip4_frags.constructor = ip4_frag_init;
        ip4_frags.destructor = ip4_frag_free;
        ip4_frags.skb_free = NULL;
        ip4_frags.qsize = sizeof(struct ipq);
        ip4_frags.match = ip4_frag_match;
        ip4_frags.frag_expire = ip_expire;
        ip4_frags.secret_interval = 10 * 60 * HZ;
        inet_frags_init(&ip4_frags);
}

EXPORT_SYMBOL(ip_defrag);